1. Field of the Invention
The present invention concerns a composite tube made of synthetic resin having a relatively small diameter of not greater than about 20 mm which is generally disposed, for example, as oil or air supplying lines in automobiles or various kinds of mechanical apparatus.
2. Description of the Prior Art
Composite tubes made of synthetic resin of the aforementioned type are for instance made of polytetrafluoroethylene (PTFE). However when the tube is put to use, rubbing is caused between the outer circumference of the tube and other parts adjacent therewith or frictional contact is caused between the tube and an inner fluid passing therethrough due to vibrations applied to the tube per se. Further, the fluctuation of fluid pressure always repeated in the inner fluid, induces electrostatic charges to the tube itself and the circumferential wall of the tube is damaged during long time use due to sparks generated by the electrostatic charges. Accordingly, there have been adopted countermeasures for removing electrostatic charges. For example, a carbon powder has been mixed directly into the tube material thereby providing the tube with electroconductivity (not illustrated). Alternatively, as shown in FIG. 6, an inner circumference 11' of a tube main body 11 made of a PTFE is laminated with a resin tube 12 rendered electroconductive by the mixing of a carbon powder 13. In the figure, reference numeral 14 denotes a braided member made of metal wires and covered on the outer circumferential surface of the tube main body 11.
Such prior art, however, requires the use of a joint made of electroconductive and chemical resistant material in contact with the tube main body 11 and in relation with the grounding mechanism at the end of the tube. This complicates the structure, increases the cost, lowers the strength of the tube to deteriorate the pressure resistance, and results in troublesome disposing operation. In the later means, since a great amount of the carbon powder is directly exposed to chamicals, in a case where the fluid incorporated in the tube comprises chemicals, the chemical resistance of the tube is deteriorated to restrict the application use. Further, when the resin tube 12 is inserted and laminated (at 13) on the inner circumferential surface 11' of the tube main body 11 upon manufacture, the adhesion at the inner circumferential surface of the tube main body 11 made of the (PTFE) is poor. Therefore the resin tube 12 tends to be peeled off easily and this remarkably makes the production complicated so as to increase the product cost, etc.